The retinal pigment epithelium of the teleost Notopterus notopterus (Pallas): appearance of basal infoldings during prolonged dark-adaptation

In teleosts, the basal part of the retinal pigment epithelium (RPE) is relatively smooth, i. e., it is free of basal membrane infoldings. In the featherback, Notopterus notopterus, whereas this is the situation in light adaptation, during dark-adaptation, especially when kept for prolonged periods (6-9 hour), numerous infoldings appear at the basal region, as found uniquely by transmission electron microscopy. In this teleost, during retinomotor movements, the rods move vitreally during dark-adaptation, while the cones do not elongate, and remain stationary in both light- and dark-adaptation. The significance of the appearance of basal infoldings in dark-adapted RPE is explained in terms of the pattern of retinomotor responses and the features of RPE and photoreceptors in this species. It is suggested that (1) the thick, impervious tapetal layer present in the RPE, (2) the unusual position of the photoreceptors in the visual cell layer of dark-adapted retina, and (3) the presumably high demand for glucose and O2 of the outer retina during dark-adaptation might contribute to cause this phenomenon in this species. The available evidence tend to associate this phenomenon with the involvement of the RPE in nutrient and O2 delivery to the photoreceptors via the basal infoldings of the RPE in dark-adapted state in this species. This has not been reported for any other teleosts to date.     

An electron microscopic study of retinal degeneration in Sprague-Dawley rats

Retinal degeneration in untreated, female Sprague-Dawley rats was studied by electron microscopy and horseradish peroxidase tracer technique. The degeneration appeared to have started at a very young age. The severity of the defect varied from a decrease of photoreceptor nuclei to total loss of receptor cells and the pigment epithelium. In mild degeneration some regions of the retinal pigment epithelium became bilayered and the basal plasma membrane became flattened or formed elaborate infoldings. Breaks in Bruch's membrane occurred in severe degeneration. Degeneration of the pigment epithelium allowed permeation of tracer material from the choroid into the retina.     

The intracytoplasmic channel in pigment epithelial cells of the chick retina

Summary The fine structure of pigment epithelial cells in the chick retina was studied by electron microscopy with a special attention to the intracytoplasmic channel which is considered to be an important passage of metabolites from the choroidal side to the vitreal side. The chick retina was fixed either by perfusion with glutaraldehyde followed by osmium tetroxide or by immersion in situ with osmium tetroxide before removal of the eyeball. The infoldings appearing in the basal zone of the retinal pigment epithelial cell were provided with the gear-like projection which was encountered as their bottom in many cases, suggesting selective absorption of proteins. It was noticed that certain interspaces of the infoldings were continuous to tubular elements of the agranular endoplasmic reticulum. Moreover, the tubular elements were found in association with such other cellular components as nuclear envelope, mitochondria, fuscin granules and plasma membrane surrounding the outer segment of photoreceptor. The pigment epithelial cell appeared to be continuous with the photoreceptor through the pores of their plasma membranes. The presence of a certain intracytoplasmic channel from the choroid to the photoreceptor is considered to facilitate the transport of metabolites in the pigment epithelial cell.Part of these observations was presented at the Sixth International Congress for Electron Microscopy, Kyoto in 1966.I wish to thank Prof. Gonpachiro Yasuzumi for his valuable advices and discussions through this study.     

Ezrin promotes morphogenesis of apical microvilli and basal infoldings in retinal pigment epithelium

Ezrin, a member of the ezrin/radixin/moesin (ERM) family, localizes to microvilli of epithelia in vivo, where it bridges actin filaments and plasma membrane proteins. Here, we demonstrate two specific morphogenetic roles of ezrin in the retinal pigment epithelium (RPE), i.e., the formation of very long apical microvilli and of elaborate basal infoldings typical of these cells, and characterize the role of ezrin in these processes using antisense and transfection approaches. In the adult rat RPE, only ezrin (no moesin or radixin) was detected at high levels by immunofluorescence and immunoelectron microscopy at microvilli and basal infoldings. At the time when these morphological differentiations develop, in the first two weeks after birth, ezrin levels increased fourfold to adult levels. Addition of ezrin antisense oligonucleotides to primary cultures of rat RPE drastically decreased both apical microvilli and basal infoldings. Transfection of ezrin cDNA into the RPE-J cell line, which has only trace amounts of ezrin and moesin, sparse and stubby apical microvilli, and no basal infoldings, induced maturation of microvilli and the formation of basal infoldings without changing moesin expression levels. Taken together, the results indicate that ezrin is a major determinant in the maturation of surface differentiations of RPE independently of other ERM family members.     

Presence and distribution of Na+/K+-ATPase in the ciliary epithelium of the rabbit

Regional differences in the localization of Na+/K+-ATPase in the ciliary epithelium of albino rabbits were studied histochemically using the method of Chayen et al. and ultra-histochemically using a cerium-based method. In addition, the incubation time necessary to achieve first signs of staining was investigated as an indication of Na+/K+-ATPase activity. In the entire pars plicata: prelenticular, postlenticular, as well as tips and valleys, staining was seen in the lateral infoldings of the non pigmented epithelium (NPE) after short incubation periods. Somewhat later, the apical cell membranes also stained. The ultrastructure of these cells, together with the staining pattern, point towards a functional significance of the NPE in active fluid secretion. The pigmented epithelium (PE) did not stain. In the iridial processes and in the area of the ciliary ridges staining first appeared in the apical cell membranes of the NPE, which form the typical ciliary channels. The basolateral infoldings of the NPE also stained, whilst the PE remained unstained. The difference in morphology and staining between pars plicata and iridial processes could indicate a difference in function, e.g. reabsorption of freshly secreted aqueous humour. In the pars plana, only the basolateral infoldings of the PE stained. A functional significance of this area in connection with the blood retina barrier is discussed.     

The fine structure of the retina in the Japanese Quail (Coturnix Coturnix Japonica). I. Pigment Epithelium and its Vascular Barrier

The uItrastructure oft he pigment epithelium and its vascular barrier was examined in the Japanese quail by electron microscopy. Most endothelial pores in the choriocapillaris appear bridged by double diaphragms. The pigment epithelium is characterized by numerous slender basal infoldings, myeloid bodies and phagosomes. Myeloid bodies communicate with the nuclear envelope and profiles of both the rough and smooth endoplasmic reticulum.Phagosome formation appears to be accomplished by concomitant activity of the rod itself (curling of apical lamellae) and the apical villi of the pigment epithelium. Within the pigment epithelium cytoplasm the phagosomes undergo degeneration and are associated with increased numbers of lysosomal-like granules.     

Presence and distribution of Na+/K+-ATPase in the ciliary epithelium of the rabbit

Summary Regional differences in the localization of Na⁺/K⁺-ATPase in the ciliary epithelium of albino rabbits were studied histochemically using the method of Chayen et al. and ultra-histochemically using a cerium-based method. In addition, the incubation time necessary to achieve first signs of staining was investigated as an indication of Na⁺/K⁺-ATPase activity. In the entire pars plicata: prelenticular, postlenticular, as well as tips and valleys, staining was seen in the lateral infoldings of the non pigmented epithelium (NPE) after short incubation periods. Somewhat later, the apical cell membranes also stained. The ultrastructure of these cells, together with the staining pattern, point towards a functional significance of the NPE in active fluid secretion. The pigmented epithelium (PE) did not stain. In the iridial processes and in the area of the ciliary ridges staining first appeared in the apical cell membranes of the NPE, which form the typical ciliary channels. The basolateral infoldings of the NPE also stained, whilst the PE remained unstained. The difference in morphology and staining between pars plicata and iridial processes could indicate a difference in function, e.g. reabsorption of freshly secreted aqueous humour. In the pars plana, only the basolateral infoldings of the PE stained. A functional significance of this area in connection with the blood retina barrier is discussed.Dedicated to Professor Dr. T.H. Schiebler on the occasion of his 65th birthday     

Radioautographic study of the cellular proliferation of retinal pigment epithelium in axolotls

The proliferative activity of the pigment epithelium cells in the axolotl eyes was studied using 3H-thymidine in two types experiments: after the removal of lens, iris and retina and upon the cultivation of the pigment epithelium pieces in the cavity of lens-less eye. Irrespective of the operation type, the level of proliferation of the pigment epithelium cells changed regularly with respect to the time of observation. In the intact eye, the level of proliferation of the pigment epithelium cells was not high: the index of labelled nuclei equaled 0.5%, no mitoses were found. The highest values of the index of labelled nuclei (12.6-32.1%) and of the mitotic index (0.54-1.07%) were registered on the 10-20th days after the operation. After 40 days, the indices of proliferative activity of the pigment epithelium cells approached gradually those for the intact eye. The cultivation of the pigment epithelium cells in the cavity of a lens-less eye for 50 days did not result in their transdifferentiation into retina cells. The layered retina found in 7.7% of cases after the removal of lens, iris and retina could regenerate either from the cells of the retina growth zone localized in the region of embryonic split, or due to transdifferentiation of the pigment epithelium cells.     

Ultrastructural study of the retinal pigment epithelium during metamorphosis in the sea lamprey (Petromyzon marinus L.)

Summary The sequence of morphological changes in the retinal pigment epithelium during the metamorphic period of the sea lamprey Petromyzon marinus L. has been investigated using electron microscopy. At early metamorphic stages (stages I and II), photoreceptors are present in a small zone of the retina. During these stages, the lateral surface of the epithelial cells shows zonulae occludentes and adhaerentes. The degree of cell differentiation varies throughout the retinal pigment epithelium. Cells covering the differentiated photoreceptors in the central retina have phagosomes, whereas pigment granules appear only in the retinal pigment epithelium dorsal to the optic nerve head. Most epithelial cells have myeloid bodies; their morphology is more complex around the optic nerve head. At stage III, when photoreceptors develop over the whole retina, the distribution of cytoplasmic organelles is almost homogeneous in the retinal pigment epithelium. Subsequently, the basal plasma membrane of the epithelial cells becomes progressively folded and their apical processes enlarged. In addition, extensive gap junctions develop between retinal pigment cells. In late metamorphic stages, noticeable growth of myeloid bodies occurs and consequently the retinal pigment epithelium resembles that of the adult. This study also describes, for the first time, the presence of wandering phagocytes in the retinal pigment epithelium of lampreys; their role in melanosome degradation is discussed.     

A new enveloped helical virus from the blue crab,Callinectes sapidus

Quite different ultrastructural changes were observed in the columnar cell and the goblet cell of the silkworm midgut after administration of the crystalline toxin of Bacillus thuringiensis. Shortly after the ingestion of the toxin, the deep infoldings of the basal cell membrane of some columnar cells became very irregular in shape and the mitochondria near the basal region were transformed into a condensed form. A few goblet cells showed relatively high electron density in the cytoplasm. The earliest pathological changes were slight and located in a region lying between the first and second thirds of the midgut. With the passage of time, they spread anteriorly and posteriorly to include the entire anterior two thirds of the midgut and became more profound. The cytoplasm of columnar cells became very electron transparent. Most mitochondria were transformed into a condensed form and the endoplasmic reticulum assumed a vacuole-like configuration. The basal infoldings of the cell membrane almost disappeared. On the other hand, the cytoplasm of the goblet cells became very electron dense and granular. The clear basal infoldings of the cell membrane were enlarged making a striking contrast with the dense cytoplasm. However, the mitochondria and the endoplasmic reticulum did not show any pathological deformation.     

Retinal pigment epithelial fine structure in the bobtail goanna (Tiliqua rugosa)

The retinal pigment epithelium (RPE), the choriocapillaris and Bruch's membrane (complexus basalis) have been studied by light and electron microscopy in the bobtail goanna (Tiliqua rugosa) an Australian diurnal lizard. The RPE consists of a single layer of cuboidal cells which display very deep and tortuous basal (choroidal) infoldings as well as numerous apical (vitreal) processes which interdigitate with the photoreceptor cells. The lateral cell borders are relatively smooth and joined by basally located tight junctions. Internally smooth endoplasmic reticulum is abundant while rough endoplasmic reticulum is not. The RPE cell nucleus is large and vesicular and basally located in the light-adapted state. Polysomes, mitochondria and myeloid bodies are present and widely distributed. Melanosomes are plentiful in the apical region of the epithelial cells in light-adaptation. Bruch's membrane is pentalaminate with the basal lamina of the choriocapillaris being exceptionally thick. The choriocapillaris is a single layer of large-caliber capillaries with thin but only moderately fenestrated endothelium. Numerous dense granules are always present within these endothelial cells.     

Responses of the retinal pigment epithelium of the mouse after acute loss of blood

Albino mice were bled through the hearts by cardiac puncture and 1/2, 1/3 and 1/4 mls of blood were taken out from 3 groups of animals. respectively. Half of the experimental animals were reinfused with 5% dextrose 1 h after bleeding. All were killed either 2, 5, 9, 24, 48 or 72 h after bleeding, and the phagosome numbers per 5 pigment cells counted and compared with control retinae. A severe decrease was evident after bleeding and the decrease leveled off 48 h afterwards. Reinfusion with dextrose had a positive beneficial effect.     

Electron microscopic observations on the retinal pigment epithelium and choroid in the domestic pig (Sus scrofa)

Summary The morphology of the retinal pigment epithelium (RPE) and adjacent choroid has been investigated by electron microscopy in the domestic pig. The RPE consists of a single layer of cells which are columnar posteriorly but become cuboidal and even squamous moving peripherally in the fundus. The cells of the RPE layer regardless of location display basal (scleral) infoldings and apical (vitreal) processes and are joined laterally by junctional complexes. Throughout the retina the epithelial cells are rich in smooth endoplasmic reticulum and mitochondria but less so in rough endoplasmic reticulum and polysomes. The epithelial nucleus is vesicular and basally located. In the superior fundus an area of the RPE is very lightly pigmented and richer in lysosomes than is this layer in the inferior and peripheral fundus. The choroid overlying this area is also lightly pigmented and contains much collagen in a lamellar arrangement. This region may represent a vestigial tapetum fibrosum. Bruch's membrane is slightly thicker posteriorly but is everywhere seen to have a pentalaminate substructure. The choriocapillaris is a single layer of large capillaries which show numerous fenestrations facing the RPE. In the superior fundus the choriocapillaris is also highly fenestrated facing the choroid.     

Ultrastructure of the Rectum Epithelial Cells in the Mosquito Larvae, Anopheles sinensis Wiedemann

ABSTRACT The Ultrastructure of rectum epithelial cells in the mosquito larvae, Anopheles sinensis Wiedemann, was studied using electron microscope. The rectal epithelium forms rectal papillae composed of the absorptive cells and the surrounding basal cells. Moreover, rectal epithelium was covered with thin cuticular intima. Apical plasma membrane of the epithelial cells had infoldings and in between them, mitochondria developed into elongated shape were attached. In addition, the membrane infoldings reach down into the cell cytoplasm to form several layers of leaflet-like prolongations. On both sides of these prolongations were also large, well-developed mitochondria. Their formation was that mitochondria were attached to 3 μm length and 4–13 layers of membrane wrinkle lump. Many spherites, which are lamelated crystals that form an illusory structure in concentric circles inside of the cytoplasm of epithelial cell were observed. Basal plasma membrane in the epithelial cells was also wrinkled to promulgate into the cytoplasm to become basal infoldings producing canaliculi in basal labyrinth formation. There were many mitochondria scattered in these formations as well. On the bottom of the epithelial cell, basal lamina was attached and between basal lamina and muscle bundle was subepithelial space, which is connective tissue. Inside the space, tracheal and nerve cells were observed.     

Immunocytochemical localization of vitamin A in the retina and pineal organ of the frog, Rana esculenta

Vitamin A immunoreactive sites were studied in the retina and pineal organ of the frog, Rana esculenta, by the peroxidase antiperoxidase, avidin-biotinperoxidase and immunogold methods. In dark-adapted material, strong immunoreaction was found in the outer and inner segments of the photoreceptor cells of both retina and pineal organ, as well as in the pigment epithelium, retinal Müller cells and pineal ependymal cells. In light-adapted retina, cones and green (blue-sensitive) rods were immunopositive. At the electron microscopic level, immunogold particles were found on the membranes of the photoreceptor outer segments as well as on the membranes of the endoplasmic reticulum and mitochondria. Individual retinal photorecptor cells exhibited strong immunoreaction in the distal portion of the inner segment, the ciliary connecting piece and the electron-dense material covering the outer segment. In the pigment epithelium, the immunolabeling varied in intensity in the basal and apical cytoplasm and phagocytosed outer segments. The immunocytochemical results indicate that retinoids (retinal, retinol and possibly retinoic acid) are present not only in the photoreceptor cells of the retina but also in those of the pineal organ. The light-dependent differences in the immunoreactivity of vitamin A underlines its essential role in the visual cycle of the photopigments. Our results suggest that the pineal ependyma plays a role comparable to that of the Müller cells and pigment epithelium of the retina with regard to the transport and storage of vitamin A. The presence of a retinoid in nuclei, mitochondria and cytoplasmic membranes suggests an additional role of vitamin A in other metabolic processes.     

Antisera to basal lamina and glial endfeet disturb the normal extension of axons on retina and pigment epithelium basal laminae

In order to determine the role of the extracellular matrix in regulating the directed growth of embryonic neurites, antisera to retina (a-RBL I and II), to pigment epithelium (a-PBL) and to glomerular (a-GBL) basal lamina were probed for an effect on the ordered extension of neurites. In the assays, retina explants from chick and quail were cultured on basal lamina from embryonic chick retina and pigment epithelium either in the presence of anti-basal lamina antisera or in the presence of the corresponding preimmune sera. In the presence of all anti-basal lamina antisera, normal extension of axons was greatly inhibited both on retina and on pigment epithelium basal lamina. The antisera affected the growth pattern and the morphology of the individual axons in two ways: in the presence of a-RBL I the short axons were less directed, developed more and longer side branches, and the lamellipodia of the growth cones were reduced in size compared to axons from control cultures. In the presence of a-RBL II and a-GBL, axons grew slowly out from the explants as very thick bundles, strikingly different from axons in control cultures. The antiserum to pigment epithelium basal lamina induced both strong fasciculation and disorganization of the linear fiber extension, being intermediate between the two types of effects observed after antiserum addition. The results suggest that adhesive matrix molecules in basal laminae have important functions in elongation, fasciculation and in the morphology of growing axons.     

Subcellular aging markers of retinal pigment epithelium in Japanese quail Coturnix japonica

Age-related changes of retinal pigment epithelium of the Japanese quail, which at present is a promising experimental model of accelerated aging, were studied by electron microscopy using morphometric analysis. It was established that, along with accumulation of lipofuscin granules and ultrastructural changes of the Bruch’s membrane, changes in the shape of nuclei and mitochondria (increase in the portion of ring-shaped and dumbbell-like mitochondria), decrease in the amount of myeloid bodies, and disorganization of basal infoldings are also aging markers of retinal pigment epithelium.     

Effect of chronic administration of sildenafil citrate (Viagra) on the histology of the retina and optic nerve of adult male rat

Background

Abnormal vision has been reported by 3% of patients treated with sildenafil citrate (Viagra). Although many men use Viagra for an extended period for treatment of erectile dysfunction, the implications of the long term-daily use of it on the retina and optic nerve are unclear.

Ocular pathology in the minimally depigmented subline of the vitiliginous Smyth chicken

Choroidal melanocytes and the retinal pigmented epithelium (RPE) were studied morphologically and histochemically in the Smyth chicken, an avian model for human vitiligo. The sequence of cytological events occurring in the ocular tissue of minimally depigmented Smyth birds was determined. Abnormalities of melanocytes and the associated inflammation was least severe in peripheral areas of the choroid and most pronounced in the back of the eye at the base of the optic nerve head. In the peripheral choroid, morphologically normal melanocytes and an occasional mononuclear leukocyte were observed. However, some of these morphologically normal melanocytes histochemically demonstrated atypical tyrosinase activity at the trans area of the Golgi apparatus. Toward the back of the eye, the melanocytes first appeared swollen and had retracting dendrites. Ultrastructurally these melanocytes demonstrated an increase in extramelanosomal cytoplasm. Later, melanocytes became spherical and had membrane bound, autophagosome-like compartments of pigment granules. As the melanocyte injury progressed, macrophages invaded the tissue and phagocytized melanocytic dendrites. These were followed by numerous plasma cells. Eventually, the back of the eye contained no pigment and was infiltrated with numerous mononuclear inflammatory cells. The retinal pigment epithelium also demonstrated a gradient in the degree of destruction, related to its topography. These cytological features consisted of the retraction of apical RPE processes, the disappearance of the basal plasma membrane infoldings, and the replacement of Bruch's membrane by collagen-like fibrils. These results demonstrate that the uveitis which develops in vitiligo appears to be a consequence of an inherent choroidal melanocyte defect.